Android群英传读书笔记

之所以会买《Android群英传》这本书，是因为阅读了任玉刚的技术博客，其中有一篇是介绍Android开发人员的进阶路径。说到《Android群英传》这本书，遂买之。

书本已经阅读完毕，总体感觉还是偏基础，知识点比较零散，适合从事Android开发的2年至3年的有经验者阅读。

个人认为的重点章节：第3章，第5章，第6章第1节、第3节，第7章，第8章，第10章

一些相对重要的代码模板：

1、自定义View

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        setMeasuredDimension(measureWidth(widthMeasureSpec), 
                measureHeight(heightMeasureSpec));
    }
    
    private int measureWidth(int measureSpec) {
        int result = 0;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);
        
        if (specMode == MeasureSpec.EXACTLY) {
            result = specSize;
        } else {
            result = 200; // 默认值
            if (specMode == MeasureSpec.AT_MOST) {
                result = Math.min(result, specSize);
            }
        }
        return result;
    }

    private int measureHeight(int measureSpec) {
        int result = 0;
        int specMode = MeasureSpec.getMode(measureSpec);
        int specSize = MeasureSpec.getSize(measureSpec);

        if (specMode == MeasureSpec.EXACTLY) {
            result = specSize;
        } else {
            result = 200; // 默认值
            if (specMode == MeasureSpec.AT_MOST) {
                result = Math.min(result, specSize);
            }
        }
        return result;
    }

2、自定义ViewGroup

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        int count = getChildCount();
        for (int i = 0; i < count; i++) {
            View childView = getChildAt(i);
            measureChild(childView, widthMeasureSpec, heightMeasureSpec);
        }
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            View child = getChildAt(i);
            if (child.getVisibility() != View.GONE) {
                child.layout(left, i * mScreenHeight,
                        r, (i + 1) * mScreenHeight);
            }
        }
    }

3、事件拦截机制

View拦截

@Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        return super.dispatchTouchEvent(event);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return super.onTouchEvent(event);
    }

ViewGroup拦截

@Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        return super.dispatchTouchEvent(ev);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        return super.onInterceptTouchEvent(ev);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return super.onTouchEvent(event);
    }

拦截流程

ViewGroup     dispatchTouchEvent
ViewGroup     onInterceptTouchEvent
View          dispatchTouchEvent
View          onTouchEvent
ViewGroup     onTouchEvent

4、SurfaceView使用

代码模板

public class SurfaceViewTemplate extends SurfaceView implements SurfaceHolder.Callback,Runnable{

    private SurfaceHolder mHolder;
    
    private Canvas mCanvas;
    
    private boolean mIsDrawing;
    
    public SurfaceViewTemplate(Context context) {
        super(context);
        initView();
    }

    public SurfaceViewTemplate(Context context, AttributeSet attrs) {
        super(context, attrs);
        initView();
    }

    public SurfaceViewTemplate(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        initView();
    }
    
    private void initView() {
        mHolder = getHolder();
        mHolder.addCallback(this);
        setFocusable(true);
        setFocusableInTouchMode(true);
        this.setKeepScreenOn(true);
    }

    @Override
    public void surfaceCreated(SurfaceHolder surfaceHolder) {
        mIsDrawing = true;
        new Thread(this).start();
    }

    @Override
    public void surfaceChanged(SurfaceHolder surfaceHolder, int i, int i1, int i2) {

    }

    @Override
    public void surfaceDestroyed(SurfaceHolder surfaceHolder) {
        mIsDrawing = false;
    }

    @Override
    public void run() {
        while (mIsDrawing) {
            draw();
        }
    }
    
    private void draw() {
        try {
            mCanvas = mHolder.lockCanvas();
        } catch (Exception e) {
            
        } finally {
            if (mCanvas != null) {
                mHolder.unlockCanvasAndPost(mCanvas);
            }
        }
    }
}

5、Activity Fragment 生命周期

四种启动模式：standard、singleTop、singleTask、singleInstance
Intent Flag 启动模式
清空任务栈：clearTaskOnLaunch、finishOnTaskLaunch、alwaysRetainTaskState

6、性能优化

布局优化
内存优化
使用工具进行分析、优化

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